All of the above. Ellipsis are generally used to indicate missing information from, before or after a quote.
1. As mentioned above, ellipsis do in fact note left out information in a quotation.
2. When an ellipsis occurs before quoted material it means that the writer has omitted text that occurs before the mentioned quote.
3. When an ellipsis occurs after quoted material it means that the writer has omitted text that occurs after the mentioned quote.